Ward v. Rock Against Racism
In Ward v. Rock Against Racism, 491 U.S. 781 (1989), the U.S. Supreme Court upheld restrictions on sound amplification in a public park:
- ... even in a public forum the government may impose reasonable restrictions on the time, place, or manner of protected speech, provided the restrictions are justified without reference to the content of the regulated speech. 
The plaintiff had argued that being ordered to turn down the volume violated their free speech rights, but the court disagreed.
- The guideline is content neutral, since it is justified without reference to the content of the regulated speech. The city's principal justification - the desire to control noise in order to retain the sedate character of the Sheep Meadow and other areas of the park and to avoid intrusion into residential areas - has nothing to do with content. 
The Court concluded that the government had a substantial interest in "protecting its citizens from unwelcome noise." Id. at 796 (quoting City Council v. Taxpayers for Vincent, 466 U.S. 789, 806 (1984)).